This has nothing to do with information design, but I thought I'd
point out what appears to be an error in your description of the
'Downs Eureka Pass' sleight of hand.

Briefly (for those who don't have the book): a magician with his
right hand makes a coin seem to vanish while in fact concealing
it behind his fingers. The left hand then openly transfers a
second coin to the right, surreptitiously taking the first, hidden
one in the process. The right hand then 'vanishes' the second
coin in the same manner as the first, and the cycle can repeat.

ET writes: "Since the left hand must hide an increasing
accumulation of potentially clinking coins, the repeated cycles
grow more difficult."

Surely, only two coins are required, and neither hand ever holds
more than one. The 'vanished' one becomes, moments later, the
next 'new' one apparently drawn from a nonexistent supply in a
pocket or other container.

The 'reverse' of this effect is to make coins 'appear' in the right
hand by essentially the same technique. The left hand in taking
the coin loads a second one into the concealed position, so
another coin can appear in the right moments later. Usually the
magician will with his left hand pretend to drop the just-
appeared coin into a metallic pail, which emits a nice loud 'clink'
to signal that the coin has hit the bottom. In fact, there's a device
hidden in the pail which creates a false noise, as the magician
conceals the first coin again in his left hand, for transport back to
the right as the cycle repeats. The audience doesn't actually see
the coins falling into the pail ("Hey, why doesn't he use a glass
bowl?") but their ears get the message, and believe.

The question is completely understandable, and indeed a good catch, based on our incomplete excerpt. Here is the complete relevant passage, which should clarify matters. Downs' claim of "not so difficult" is questionable, as is, in fact, his claimed ability to successfully execute this with 20 coins, which seems unlikely, even for a man of Downs' remarkable skills.

"The author has extreme pleasure, in the following description of the pass to which he has given the above title, in taking the reader into his confidence [...] and explaining to him fully what the writer conscientiously believes to be his most novel, puzzling and prettiest feat:

The pass is used for the vanishing of any number of coins, up to 20, one at a time.

The coins are lying on the table. One is placed in the right hand is in fig.1 (in readiness for the back palm). This is made and both hands shown (apparently) empty. The left hand now picks up another coin by the first finger and thumb, and proceeds to place it on the right hand in the position occupied by the first (see fig. 28), but in the act of doing so the middle fingers of the left hand go to the back of the right and remove the first coin (see fig. 29). The left hand now leaves the second coin on the right hand, which back palms it, the left hand in the meantime palming coin No. 1.

This is repeated until the whole of the coins are palmed in the left hand.Of course, considerable practice is necessary to palm the coins one after the other without noise, but this is not so difficult if the first coin is palmed as per fig. 9, and each following one is placed under the preceding one."

Forgive the extremely late response, but I came across this thread and just want to add a thought. Historically speaking, there is reason to believe that the very purpose of Downs book -- his first, which was sold as a souvenir to spectators who attended his shows -- was to emphasize the difficulty of the sleights, rather than teach them. Downs, whose talent with coins was legendary, distributed these books, which arguably "exposed" the very effects he was perforrming, to showcase his unusual skill. This may explain, in part, why the books explanations may, at times, been less than transparent and the choice of more difficult means of accomplishing an effect.